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Bullpup Rifles (Auto & Semi-Auto Centerfire) => Tavor7 => Topic started by: Tvfreakarms on July 28, 2018, 04:29:22 PM



Title: Short stroke Vs long stroke
Post by: Tvfreakarms on July 28, 2018, 04:29:22 PM
What was the point of changing the tavor from long to short stroke gas piston on their tavor 7?

The big thing for me is, I'm also wondering where the excess gasses get expelled out of?

Is it out and front of the muzzle area or is it still shots the gasses back into the inside rec? What the sar/x95 and even the MDR from what I read.

Especially shooting it suppressed. Im sure we all seen the videos of how pretty nasty it gets inside the tavor.
Makes a Di AR rifle  clean 😂.

LLAP



Title: Re: Short stroke Vs long stroke
Post by: DOWNS on July 28, 2018, 09:22:08 PM
I'd imagine that if they need less gas they will make the gas port smaller or if it has an adjustable gas valve make the ports on that smaller.


Title: Re: Short stroke Vs long stroke
Post by: HBeretta on July 29, 2018, 03:37:50 AM
What was the point of changing the tavor from long to short stroke gas piston on their tavor 7?

Less gas and less recoil which makes sense in 308 with higher cyclic rate in full auto.  Consensus is long stroke is more reliable...it seems, but weíre talking the Toyota of firearms here in IWI.


Title: Re: Short stroke Vs long stroke
Post by: Tvfreakarms on July 29, 2018, 05:29:41 AM
Does anyone know where the excess gasses escapes?
Is it inside the rec or shots out toward the muzzle?
From what I read, and seen slow motion, it seems it still escapes inside the rec. Which I don't get.

LLAP



Title: Re: Short stroke Vs long stroke
Post by: HBeretta on July 29, 2018, 07:51:20 AM
Does anyone know where the excess gasses escapes?
Is it inside the rec or shots out toward the muzzle?
From what I read, and seen slow motion, it seems it still escapes inside the rec. Which I don't get.

LLAP



you have gas escaping from the gas cylinder which unfortunately is located further back(closer to shooters face) on an x95/tavor - see below vid that was thrown up recently with regard to this.  the gas cylinder on an rdb for example is located further up on the rifle closer to the muzzle, and especially on an fs2000.  the major advantage with the rdb with regard to excess gas is how you can fine tune the gas to the ammo being used along with the receiver design minimizing excess/residual gas in the shooters face as it escapes through the downward ejection chute - especially when suppressed.  you mentioned suppressed and assumed gas blowback due to the baffles sending gas backwards.  oss threw up a vid few years back along with MAC recently speaking to eliminating this in his MDR vid - see below.  now i'm curious as to the internal design of the t7, but it appears the gas cylinder is further up or closer to the muzzle in looking at photos...the gas adjustment knob being the giveaway.  from there i guess it's rifle design as to how residual gasses flow out of the receiver; alibrando speaks to this in the tavor vid below...some users complaining it seeping through the butt-pad on the MDR and so on.  anyway, not sure if this helps.

x95 gas reduction
https://www.youtube.com/watch?v=5FDOXK2p0N0 (https://www.youtube.com/watch?v=5FDOXK2p0N0)

gas blowback
https://www.youtube.com/watch?v=c0uYVFj_M8Y (https://www.youtube.com/watch?v=c0uYVFj_M8Y)

rdb suppressed efficiency (gas venting downward)
https://youtu.be/ESGwQS-JW40?t=7m46s (https://youtu.be/ESGwQS-JW40?t=7m46s)



Title: Re: Re: Short stroke Vs long stroke
Post by: Tvfreakarms on July 29, 2018, 08:02:18 AM
Interesting.
I know there was a lot of complaints about the sar/x95 having the gas face from the gas port. I was really surprised how much of it when it was suppressed.
Hopefully iwi fixed this issue. By having the gas going out or it's toward the muzzle.
I believe Adams arm's piston rifles shoots gas out the front toward the muzzle.
Does anyone know where the excess gasses escapes?
Is it inside the rec or shots out toward the muzzle?
From what I read, and seen slow motion, it seems it still escapes inside the rec. Which I don't get.

LLAP



you have gas escaping from the gas cylinder which unfortunately is located further back(closer to shooters face) on an x95/tavor - see below vid that was thrown up recently with regard to this.  the gas cylinder on an rdb for example is located further up on the rifle closer to the muzzle, and especially on an fs2000.  the major advantage with the rdb with regard to excess gas is how you can fine tune the gas to the ammo being used along with the receiver design minimizing excess/residual gas in the shooters face as it escapes through the downward ejection chute - especially when suppressed.  you mentioned suppressed and assumed gas blowback due the the baffles sending gas backwards.  oss threw up a vid few years back along with MAC recently speaking to eliminating this in his MDR vid - see below.  now i'm curious as to the internal design of the t7, but it appears the gas cylinder is further up or closer to the muzzle in looking at photos...the gas adjustment knob being the giveaway.  from there i guess it's rifle design as to how residual gasses flow out of the receiver; alibrando speaks to this in the tavor vid below...some users complaining it seeping through the butt-pad on the MDR and so on.  anyway, not sure if this helps.

x95 gas reduction
https://www.youtube.com/watch?v=5FDOXK2p0N0 (https://www.youtube.com/watch?v=5FDOXK2p0N0)

gas blowback
https://www.youtube.com/watch?v=c0uYVFj_M8Y (https://www.youtube.com/watch?v=c0uYVFj_M8Y)

rdb suppressed efficiency (gas venting downward)
https://youtu.be/ESGwQS-JW40?t=7m46s (https://youtu.be/ESGwQS-JW40?t=7m46s)

LLAP



Title: Re: Short stroke Vs long stroke
Post by: BullpupT on July 31, 2018, 08:01:14 AM
Recoil is reduced with short stroke systems due to the use of lighter bolt assemblies. They have less reciprocating mass which helps with faster follow up shots.

Think of it like an AK/PSL vs. SVD. The both look very similar yet they are completely different. You get much faster follow up shots with a lighter short stroke bolt.


Title: Re: Short stroke Vs long stroke
Post by: blottogg on July 31, 2018, 11:23:36 PM
With the two-stage, long stroke piston on the original Tavor, the cylinder extends almost to the breach of the barrel, and the piston actually clears the cylinder at the end of the bolt carrier's travel, dumping any residual gas into the guts of the receiver.  Unsuppressed, the piston/recoil spring, etc. are designed so that there's little gas pressure remaining at the full length of travel, so not much gets dumped into the shooter's face.  Suppressed, there's more gas fed to the cylinder, and that excess gas dumps into the receiver like a DI AR.  From what I've seen of the Tavor 7, the short-stroke piston doesn't extend nearly as far towards the breech as the long stroke setup (as you'd guess from the names), the gas being confined to a smaller cylinder in what you can think of as a big gas block towards the barrel (there's a push rod transferring the motion to the bolt carrier, without any plumbing for gas).  the valve adjustment knob for the gas cylinder is on the front of this block, so I'm assuming that the vent for any excess gasses is on the front of the block also, and should vent forward.  That there's a setting for suppressors on the adjustment knob also means that less gas is being tapped from the barrel on that setting, which should prevent any over-gassing to begin with.

The main differences between short and long stroke gas piston setups are that long-stroke is mechanically simpler (the piston is part of the bolt carrier group) and self-regulating (over-gassing just gets vented at the end of the piston's stroke, though as noted, that can leave a mess), while the short-stroke setup is more expensive (more parts to make) and cleaner, with the gasses confined to a smaller cylinder at the front of the weapon, and can be made adjustable with a valve at the gas port.  I guess you could make long-stroke systems adjustable with a valve as well, but I haven't seen a setup like that.


Title: Re: Re: Short stroke Vs long stroke
Post by: Tvfreakarms on August 01, 2018, 12:07:25 AM
Interesting. I was just curious of where the excess gasses are going to be dumped.

My thinking was why make a piston rifle that will dump excess gasses back into the rifle this creating more gasses potentially in the face and make the rifle really dirty. Especially when it's suppressed.
I know there is a youtuber who showed what it looked like afterwards. I don't think I've seen a dirtier rifle.
With the two-stage, long stroke piston on the original Tavor, the cylinder extends almost to the breach of the barrel, and the piston actually clears the cylinder at the end of the bolt carrier's travel, dumping any residual gas into the guts of the receiver.  Unsuppressed, the piston/recoil spring, etc. are designed so that there's little gas pressure remaining at the full length of travel, so not much gets dumped into the shooter's face.  Suppressed, there's more gas fed to the cylinder, and that excess gas dumps into the receiver like a DI AR.  From what I've seen of the Tavor 7, the short-stroke piston doesn't extend nearly as far towards the breech as the long stroke setup (as you'd guess from the names), the gas being confined to a smaller cylinder in what you can think of as a big gas block towards the barrel (there's a push rod transferring the motion to the bolt carrier, without any plumbing for gas).  the valve adjustment knob for the gas cylinder is on the front of this block, so I'm assuming that the vent for any excess gasses is on the front of the block also, and should vent forward.  That there's a setting for suppressors on the adjustment knob also means that less gas is being tapped from the barrel on that setting, which should prevent any over-gassing to begin with.

The main differences between short and long stroke gas piston setups are that long-stroke is mechanically simpler (the piston is part of the bolt carrier group) and self-regulating (over-gassing just gets vented at the end of the piston's stroke, though as noted, that can leave a mess), while the short-stroke setup is more expensive (more parts to make) and cleaner, with the gasses confined to a smaller cylinder at the front of the weapon, and can be made adjustable with a valve at the gas port.  I guess you could make long-stroke systems adjustable with a valve as well, but I haven't seen a setup like that.

LLAP



Title: Re: Short stroke Vs long stroke
Post by: BullpupT on August 01, 2018, 08:00:03 AM
With the two-stage, long stroke piston on the original Tavor, the cylinder extends almost to the breach of the barrel, and the piston actually clears the cylinder at the end of the bolt carrier's travel, dumping any residual gas into the guts of the receiver.  Unsuppressed, the piston/recoil spring, etc. are designed so that there's little gas pressure remaining at the full length of travel, so not much gets dumped into the shooter's face.  Suppressed, there's more gas fed to the cylinder, and that excess gas dumps into the receiver like a DI AR.  From what I've seen of the Tavor 7, the short-stroke piston doesn't extend nearly as far towards the breech as the long stroke setup (as you'd guess from the names), the gas being confined to a smaller cylinder in what you can think of as a big gas block towards the barrel (there's a push rod transferring the motion to the bolt carrier, without any plumbing for gas).  the valve adjustment knob for the gas cylinder is on the front of this block, so I'm assuming that the vent for any excess gasses is on the front of the block also, and should vent forward.  That there's a setting for suppressors on the adjustment knob also means that less gas is being tapped from the barrel on that setting, which should prevent any over-gassing to begin with.

The main differences between short and long stroke gas piston setups are that long-stroke is mechanically simpler (the piston is part of the bolt carrier group) and self-regulating (over-gassing just gets vented at the end of the piston's stroke, though as noted, that can leave a mess), while the short-stroke setup is more expensive (more parts to make) and cleaner, with the gasses confined to a smaller cylinder at the front of the weapon, and can be made adjustable with a valve at the gas port.  I guess you could make long-stroke systems adjustable with a valve as well, but I haven't seen a setup like that.

There are companies that make long stroke rifles with adjustable gas systems. My Daewoo rifle has an FAL style gas plug with the AK style long stroke bolt carrier.


Title: Re: Short stroke Vs long stroke
Post by: Jwill on November 09, 2018, 03:08:27 AM
I personally think that short stroke gas systems are superior for two main reasons one less reciprocating mass and the second is that the gas is vented outside of the receiver. My tavor is the dirtiest rifle that I have ever shot my bren 805 and gas piston ar however stay very clean.


Title: Re: Short stroke Vs long stroke
Post by: Halmbarte on January 02, 2019, 04:50:58 PM
The 556 Tavor does have a gas relief hole that vents high pressure gas once the gas piston has started to move back. It's located under the gas tube almost at the rear.

That said, how much gas fouling gets into the receiver depends on the design. Many designs deliberately unlock the bolt while there is still significant gas pressure in the bore. The pressure is used to accelerate the bolt backwards for reliability and/or to increase cyclic rate.

(https://i.imgur.com/OIrGmQN.jpg)

(https://i.imgur.com/8G30LhY.jpg)

(https://i.imgur.com/vPPahDr.jpg)

(https://i.imgur.com/8FPeoUa.jpg)

H


Title: Re: Short stroke Vs long stroke
Post by: Tvfreakarms on January 02, 2019, 05:50:04 PM
That's 1 of the things I don't like about the tavor piston system.  Blowing the excess gases back inside the rec. Why design it that way. Same goes for the for the MDR.

Lazy asses 😂. I rather have the excess gases go out and away from the shooters.
Bit that's my 2 cents.

Does anyone know if the tavor 7 has the excess gases go out and away from the shooters?

LLAP



Title: Re: Short stroke Vs long stroke
Post by: BullpupT on January 02, 2019, 06:14:30 PM
The AR series shoot gasses directly into the bolt carrier. Itís done on purpose, letís not forget that carbon is a lubricant. Eugene Stoner knew exactly what he was doing.



Title: Re: Re: Short stroke Vs long stroke
Post by: Tvfreakarms on January 02, 2019, 07:31:08 PM
The AR series shoot gasses directly into the bolt carrier. Itís done on purpose, letís not forget that carbon is a lubricant. Eugene Stoner knew exactly what he was doing.
I c. But the whole rec doesn't need all that carbon. Obviously a piston system is going to have carbon build up regardless. But to have the whole inside of the rec to be gunked up is not fun to clean. Especially if u cant get inside the rec system easily.

But there a good lubes out there that will work good.


LLAP



Title: Re: Short stroke Vs long stroke
Post by: Halmbarte on January 02, 2019, 07:45:46 PM
That's 1 of the things I don't like about the tavor piston system.  Blowing the excess gases back inside the rec. Why design it that way. Same goes for the for the MDR.

Lazy asses 😂. I rather have the excess gases go out and away from the shooters.
Bit that's my 2 cents.

Does anyone know if the tavor 7 has the excess gases go out and away from the shooters?

LLAP



The gas vent shown above is on the Ďdirtyí side of the receiver in font of the dirt guard that blocks debris from getting into the action.

A short stroke gas system would be more complex, and the Tavor is rather ruthlessly engineered to be simpler than an AK.

H


Title: Re: Re: Short stroke Vs long stroke
Post by: Tvfreakarms on January 02, 2019, 07:53:21 PM
That's 1 of the things I don't like about the tavor piston system.  Blowing the excess gases back inside the rec. Why design it that way. Same goes for the for the MDR.

Lazy asses 😂. I rather have the excess gases go out and away from the shooters.
Bit that's my 2 cents.

Does anyone know if the tavor 7 has the excess gases go out and away from the shooters?

LLAP



The gas vent shown above is on the Ďdirtyí side of the receiver in font of the dirt guard that blocks debris from getting into the action.

A short stroke gas system would be more complex, and the Tavor is rather ruthlessly engineered to be simpler than an AK.

H
The tavor 7 is a short stroke system.
And there are other brands of rifles that are short stroke. You already knows this. But they seem to work fine for the most part.
Some has been battle tested.
Couldn't a short stroke system made simplier?

LLAP



Title: Re: Short stroke Vs long stroke
Post by: Halmbarte on January 02, 2019, 10:49:01 PM
I was referring to the original 556 Tavor and its long stroke gas piston. I haven't seen any details of the Tavor 7's gas system. A short stroke system is pretty much always going to have a additional part (separate gas piston) and frequently as gas plug or regulator (although a long stroke system can have a gas regulator, like on the BREN). As an example, the AUG has 3 parts in it that just aren't present on the 556 Tavor: Gas regulator, gas piston, and the gas piston return spring.

After having shot the AUG and Tavor at our local rifle match for a while, my take is that the AUG's short stroke gas system is more complex and offers more opportunities for the user to lose parts in the field. The up side to those extra parts is that the AUG has an adjustable gas regulator, plus the end of the piston offers a place to split the action to accommodate the quick change barrel.

Which is better depends on what you consider more valuable: no small parts to lose or flexibility.

H


Title: Re: Re: Short stroke Vs long stroke
Post by: Tvfreakarms on January 03, 2019, 01:56:23 AM
I was referring to the original 556 Tavor and its long stroke gas piston. I haven't seen any details of the Tavor 7's gas system. A short stroke system is pretty much always going to have a additional part (separate gas piston) and frequently as gas plug or regulator (although a long stroke system can have a gas regulator, like on the BREN). As an example, the AUG has 3 parts in it that just aren't present on the 556 Tavor: Gas regulator, gas piston, and the gas piston return spring.

After having shot the AUG and Tavor at our local rifle match for a while, my take is that the AUG's short stroke gas system is more complex and offers more opportunities for the user to lose parts in the field. The up side to those extra parts is that the AUG has an adjustable gas regulator, plus the end of the piston offers a place to split the action to accommodate the quick change barrel.

Which is better depends on what you consider more valuable: no small parts to lose or flexibility.

H
Oh I c. Is was would be nice if they made a short stroke with 1 piece if possible.
The tavor 7 is a short stroke FYI.

LLAP



Title: Re: Short stroke Vs long stroke
Post by: Halmbarte on January 03, 2019, 12:35:45 PM
I'm not sure if a short stroke gas system with one piece is possible, I can't think of any examples.

W/o having a gas plug in front you need something to keep the piston from blowing out the rear of the gas cylinder. You could use  a stop, but that stop has to be removable to assemble the piston and to remove it for cleaning, so extra parts are needed.

With a gas plug in front, you're back to extra parts.

Long stroke does have advantages too. You get to add the mass of the gas piston to the bolt carrier mass, improving the BCG to bolt mass ratio, which helps with reliability. As mentioned before, it's simpler, which has intrinsic advantages too.

I'd really like to see how IWI implemented the Tavor 7 gas system to see what they thought were good design compromises. After all, all designs are a compromise, great designs (like the Tavor) come from getting the compromises right.

H


Title: Re: Re: Short stroke Vs long stroke
Post by: Tvfreakarms on January 03, 2019, 01:19:59 PM
I'm not sure if a short stroke gas system with one piece is possible, I can't think of any examples.

W/o having a gas plug in front you need something to keep the piston from blowing out the rear of the gas cylinder. You could use  a stop, but that stop has to be removable to assemble the piston and to remove it for cleaning, so extra parts are needed.

With a gas plug in front, you're back to extra parts.

Long stroke does have advantages too. You get to add the mass of the gas piston to the bolt carrier mass, improving the BCG to bolt mass ratio, which helps with reliability. As mentioned before, it's simpler, which has intrinsic advantages too.

I'd really like to see how IWI implemented the Tavor 7 gas system to see what they thought were good design compromises. After all, all designs are a compromise, great designs (like the Tavor) come from getting the compromises right.

H
That's what I read that the tavor 7 is a short stroke.  I doubt it's a 1 piece design.
I wonder why they moved away from long to the short.
And your right I think most short stroke gas at least 2 to 3 parts. I know my pof USA rifle has 3 parts.
But it would be nice if they make it 1 part and integrate the gas plug.

LLAP


Title: Re: Short stroke Vs long stroke
Post by: konigstigerii on January 03, 2019, 05:55:35 PM
My best guess is they moved to a short stroke piston to reduce the reciprocating mass to reduce felt recoil. (similar to light weight Ar15 bgc in competition use) The Tavor has no gas adjustment, so to make it reliable, its over gassed quite a bit, and the heavy mass of the bcg would make it less sensitive to gas port pressure and crud in the receiver, perfect for general issue to the masses with no interest in firearms...no settings, reliable, albeit over gassed with excess recoil (though not excess in respect to control-ability). The Tavor 7 is seemingly marketed to those more familiar with firearms, and those willing to understand its use, so a lighter mass bcg, and gas adjustment is preferable so we can tune it to run nice and smooth. 

My X95 has a prototype gas adjustment and when tuned it runs a lot smoother... like night and day compared to stock system.

The 7 gas system probably has a few parts, but its not that many more that a long stroke piston. The Tavor has the piston head, the piston tube, a roll pin, and a pin holding the piston tube to the carrier. My ACR has a piston, return spring, and a gas plug. So while the Tavor has technically 4 parts the ACR has 3 (minus common parts such as the gas block, trunnion etc). The tavor parts are simpler but not by any long shot. So its not necessarily true that all long stroke systems have fewer parts or is simpler to make.


Title: Re: Short stroke Vs long stroke
Post by: Halmbarte on January 03, 2019, 06:29:17 PM
Itís kind of reaching to count parts that are semi-permanently assembled like the 556 Tavors gas piston and gas piston tube as separate parts.

Since those parts canít be removed without tools Iím arguing they should be excluded from a normal parts count.

H


Title: Re: Re: Short stroke Vs long stroke
Post by: Tvfreakarms on January 03, 2019, 06:41:25 PM
My best guess is they moved to a short stroke piston to reduce the reciprocating mass to reduce felt recoil. (similar to light weight Ar15 bgc in competition use) The Tavor has no gas adjustment, so to make it reliable, its over gassed quite a bit, and the heavy mass of the bcg would make it less sensitive to gas port pressure and crud in the receiver, perfect for general issue to the masses with no interest in firearms...no settings, reliable, albeit over gassed with excess recoil (though not excess in respect to control-ability). The Tavor 7 is seemingly marketed to those more familiar with firearms, and those willing to understand its use, so a lighter mass bcg, and gas adjustment is preferable so we can tune it to run nice and smooth. 

My X95 has a prototype gas adjustment and when tuned it runs a lot smoother... like night and day compared to stock system.

The 7 gas system probably has a few parts, but its not that many more that a long stroke piston. The Tavor has the piston head, the piston tube, a roll pin, and a pin holding the piston tube to the carrier. My ACR has a piston, return spring, and a gas plug. So while the Tavor has technically 4 parts the ACR has 3 (minus common parts such as the gas block, trunnion etc). The tavor parts are simpler but not by any long shot. So its not necessarily true that all long stroke systems have fewer parts or is simpler to make.
Do you know if they make a prototype gas adjustment for the sar?

LLAP



Title: Re: Short stroke Vs long stroke
Post by: konigstigerii on January 08, 2019, 03:31:43 PM
No, I have one on my X95 that I've been working on  ;)



Title: Re: Short stroke Vs long stroke
Post by: konigstigerii on January 08, 2019, 03:32:47 PM
Itís kind of reaching to count parts that are semi-permanently assembled like the 556 Tavors gas piston and gas piston tube as separate parts.

Since those parts canít be removed without tools Iím arguing they should be excluded from a normal parts count.

H

That is true to a degree, but those parts still have to be engineered, spec'd, manufactured, inspected and installed.


Title: Re: Short stroke Vs long stroke
Post by: Halmbarte on January 10, 2019, 08:49:51 PM
Simpler from a parts count perspective isn't necessarily always better.

As an example, I offer the recoil spring assembly of the AK47. It contains the dust cover latch/support, the rear tube, front rod, recoil spring, and the retainer. The assembly requires machining, brazing, and swaging steps for manufacturing.

The end result is a more complex assembly for the factory to manufacture and assemble, but the end user gets one piece that stays together, is more difficult to lose, and combines the function of the recoil spring guide, captive recoil spring, and take down latch.

H


Title: Re: Short stroke Vs long stroke
Post by: konigstigerii on January 10, 2019, 08:59:02 PM
Exactly, kinda like the pins on an AR15 vs a HK G36, the pins on the AR are retained, so they are hard to loose, where as the HK pins, while simpler, can be easily lost in the field